High molecular weight linear polyesters including copolyesters of glycols with terephthalic and isophthalic acids have been available for many years. Certain of these are described in Whinfield et al., U.S. Pat. No. 2,465,319 and in Pengilly U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
With the development of molecular weight control, the use of nucleating agents and two-step molding cycles, poly(ethylene terephthalate) has become an important constituent of injection moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is outstandingly useful as a component of such compositions. Workpieces molded from such polyester resins, alone or combined with reinforcements, in comparison with other thermoplastic moldings, possess a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction. Molded articles find use in radio and television applications and as housings for electrical hand tools and industrial and kitchen appliances.
Stable polyblends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) can be molded into useful unreinforced and reinforced articles; see Fox and Wambach U.S. Pat. No. 3,953,394.
Block copolyesters containing units derived from poly(1,4-butylene terephthalate) and from an aromatic/aliphatic or aliphatic polyester are also known; see copending application Ser. No. 752,325 filed on Dec. 20, 1976, now abandoned by Borman et al. Such block copolyesters are useful alone as molding resins and also in intimate combination with poly(1,4-butylene terephthalate) and/or poly(ethylene terephthalate).
It has been proposed to increase the impact strengths of moldings prepared from polyesters by adding various modifiers. For example, Brinkmann et al., in U.S. Pat. No. 3,591,659 disclose that a useful family of modifiers comprises polyalkyl acrylates, methacrylates and/or ethacrylates. Nakamura et al. in U.S. Pat. No. 3,864,428 propose polyarylene carbonates and certain graft copolymers of polybutadiene; Seydl et al. in U.S. Pat. No. 3,937,757 and Lane in U.S. Pat. No. 4,034,013 propose polyethylene for the purpose; Baron et al., in U.S. Pat. No. 4,044,073 disclose that a useful impact modifier for such polyesters is an aromatic polycarbonate; Schlichting et al. in U.S. Pat. No. 4,022,748 disclose that a rubber-elastic graft copolymer having a glass temperature below -20.degree. C. is a useful modifier; Lane, U.S. Pat. No. 4,034,013 and Farnham et al., U.S. Pat. No. 4,096,202 disclose that useful impact modifiers comprise multiple state polymers having a rubbery first stage and a hard final stage, preferably including units derived from alkyl acrylates; Lane U.S. Pat. No. 4,034,013 discloses isotatic 1-polybutylene; Baron et al. in U.S. Pat. No. 4,034,016 disclose an impact modifier combination comprising a mixture of a polyurethane and an aromatic polycarbonate; Goedde et al. in U.S. Pat. No. 4,203,887 discloses an impact modifier combination comprising a segmented block copolyester and an aromatic polycarbonate; and Cohen et al. copending application Serial. No. 957,801 filed on Nov. 6, 1978, now U.S. Pat. No. 4,257,937 discloses that a combination of a polyacrylate resin and an aromatic polycarbonate resin is suitable for the purpose.
All of the foregoing patents and patent applications are hereby incorporated herein by reference.
The discoveries have now been made that polybutylene terephthalate-based molding compositions are compatible with cis-polybutadiene, poly(butadiene-acrylonitrile) and poly(isobutylene-isoprene), and that such molding compositions which contain a minor proportion of one or more of the above-mentioned vinyl polymers provide molded articles with greatly improved resistance to fracture upon impact.
Further discoveries have been made that the foregoing compositions are compatible with the aromatic polycarbonates and that the presence of a minor amount of one or more of these polycarbonates in the molding composition provides molded articles of even better resistance to fracture upon impact.
The aforementioned vinyl polymers consist essentially of carbon-to-carbon chains which contain residual olefinic unsaturation and which carry only hydrogen, vinyl, isopropenyl, methyl, and/or nitrile as their substituents. Other substituents, for example chloro, carboxymethyl, phenyl and methoxy can be present, which can be provided by adding the appropriate copolymerizable vinyl monomers to the mixtures from which the polymers are prepared, in such small proportion as not to alter the essential character of the polymer. Best results to date have been obtained when the polymer chains contain one point of olefin unsaturation for every 10 to 100 chain carbon atoms, when the chains contain at least one substituent for every two chain carbon atoms, and when these substituents are methyl and nitrile substituents in 10:1 to 100:1 molar ratio. The reason why the polymers described above are so effective in imparting fracture resistance to the moldings is not known, and applicants do not wish to be bound by any theory.